Cell therapy is a group of new techniques that rely in particular on replacing diseased or dysfunctional cells with healthy, functioning ones. Moreover, cell therapy finds applications in immunotherapy, involving lymphocytes. These new techniques are being applied to a wide range of human diseases, including many types of cancer, neurological diseases such as Parkinson's and Lou Gehrig's Disease, spinal cord injuries, and diabetes, auto-immune or inflammatory diseases.
Cells are the basic building blocks of the human body and hold many of the keys to how the body functions. Cells serve both a structural and a functional role in the body, performing an almost endless variety of actions to sustain the body's tissues and organs. There are hundreds, perhaps thousands, of different specialized cell types in the adult body. All of these cells perform very specific functions for the tissue or organ they compose. These mature cells have been differentiated, or dedicated, to performing their special tasks.
Bone marrow transplants are an example of cell therapy in which stem cells in a donor's marrow are used to replace the blood cells of the victims of leukemia and other cancers. Cell therapy is also being used in experiments to graft new skin cells to treat serious burn victims, and to grow new corneas for the sight-impaired. In all of these uses, the goal is for the healthy cells to become integrated into the body and begin to function like the patient's own cells. Furthermore, many studies are currently under process for priming and expanding T lymphocytes to use them as an immunotherapeutic treatment for cancer and infectious diseases, among others.
However, there are several scientific challenges that must be overcome in the field of cell therapy. One of the challenges is to provide expansion/differenciation systems for inducing a cell population to rapidly proliferate for a long term and in a sufficient quantity. For example, in T cell immunotherapy clinical trials, billions of cells have to be used. In order to produce these quantities of cells, 1000-4000 fold expansion of cells is usually required. Furthermore, for optimal engraftment potential and possible therapeutic benefit, it is important to ensure that the cells, after in vitro expansion, are functional, not senescent and not contaminated at the time of administration in a patient.
One possibility to obtain a cell population of interest is its identification from a biological sample, based on the determination of the presence of markers specific for the cell population in question, and then to proceed to its enrichment by eliminating cells that do not express the specific markers. However, such a method does not provide a sufficient quantity of cells for therapy or research purposes. Thus, there is a need for a cell production system wherein said cells may be differenciated and/or expanded, such as a cell expansion system capable to maintain exponential growth of a cell population for at least two or three months in vitro, and to have a very well characterized cell population for injection purposes, in contrast to a mixed cell population enriched with the required cells but contaminated with cells which may have adverse effects.
In the field of immunotherapy, methods of cloning and expanding T cells have proven to have certain drawbacks, including apoptosis and long-term culture (several months required) to obtain a sufficient number of cells from a single clone. It has been previously shown that magnetic beads coated with anti-CD3 and anti-CD28 antibodies can be used as artificial antigen presenting cells (aAPCs) to support the long-term growth of CD4+ T cells (see the american patent published on Mar. 5, 2002 with the number U.S. Pat. No. 6,352,694). However, beads or plates coated with anti-CD3 and anti-CD28 antibodies cannot support long-term growth of purified CD8+ T cells, and include other limitations, such as the high cost of the beads, the labor intensive process involved in removing the beads from the culture medium before infusion, and the fact that the bead based system is restricted by a need for GM (Good Manufacturing) quality control approval before the start of each application.
The american patent application published on Aug. 7, 2003 with the number US 2003/0147869 discloses the use of aAPCs engineered by the inventors to mimic dendritic cells in their ability to stimulate rapid CTL growth. According to this patent application, the K562 erythromyeloid cell line is used because it (1) is of human origin; (2) lacks MHC class I and II molecules to avoid allogeneic response; (3) grows well using serum free medium; (4) has been extensively used in the literature (over 5700 references); (5) has been characterized cytogenetically; and (6) has been approved for phase I clinical trials.
Indeed, eucaryotic cells, rather than procaryotic cells, are usually preferred since expression of eucaryotic proteins in eucaryotic cells can lead to partial or complete glycosylation and/or formation of relevant inter- or intra-chain disulfide bonds of a recombinant protein.
A major drawback correlated with the use of such aAPCs is that it is necessary to proceed to their irradiation before contacting them with the cell population to be expanded, in order to stop their growth. This irradiation requires to stimulate repeatedly the cell population to be expanded, and leads to the eventual introduction of irradiated aAPC into the clinical setting. Furthermore, the irradiation of aAPC can lead to genetic mutations, which can lead to the production of non-desirable factors. Such mutations may not be controlled and it is not possible to be totally sure that the proliferation has stopped the proliferation of all the aAPC.
Another drawback correlated with the use of eucaryotic aAPC is that these cells may allow the proliferation of eukaryotic viruses present in the cell population to be expanded.